In the first generation of single mode optical transmission networks, low loss single mode optical fibers were deployed in point to point links with directly modulated single mode lasers. A laser is directly modulated when its drive current is directly subjected to a modulating signal. For intercity transmissions where long repeater spacing and high bit rate communications are of primary concern, this is an effective and efficient use of single mode technology. However, for short haul communications, the typical distance between a central office or other communications center and a user station is much shorter than the maximum available repeater spacing. In this environment, the use of a directly modulated laser for each communication link between a central office and an end user represents a considerable waste of laser power.
One way to more efficiently use single mode lasers and single mode optical fibers in a short haul system is to share a single laser among a plurality of communications links. Laser sharing schemes for use in single mode short haul optical transmission systems are disclosed in U.S. patent application Ser. No. 680,398 filed on behalf of S. S. Cheng, J. Lipson, and S. D. Personick, now U.S. Pat. No. 4,658,394, issued Apr. 14, 1987, U.S. patent application Ser. No. 732,556 filed on behalf of S. D. Personick, now U.S. Pat. No. 4,642,804, issued Feb. 10, 1987, and U.S. patent application Ser. No. 777,952 filed on behalf of S. S. Cheng on even date herewith. All of the aforementioned applications are assigned to the assignee hereof and are incorporated herein by reference.
The systems described in the above-mentioned patent applications utilize single mode technology including single mode lasers and single mode optical fibers, to transmit information from a central office to a plurality of user stations and from a user station back to the central office. However, none of these applications deal with the problem of how to establish a network which will enable communication between pairs of user stations and which will enable a single user station to broadcast information to a plurality of other user stations.
Accordingly, it is an object of the present invention to provide a short haul optical communication system using single mode technology which permits point to point connections between pairs of user stations and which permits a single user station to broadcast information to a plurality of other user stations. Such a network will be useful in a local access and transport area (LATA) or a local area network (LAN).